The present invention relates generally to surgical procedures for spinal stabilization and more specifically to instrumentation adapted for inserting a spinal implant within the intervertebral disc space between adjacent vertebra. More particularly, while aspects of the invention may have other applications, the present invention is especially suited for disc space preparation and inmplant insertion into a disc space form a generally anterior approach to the spine.
Various surgical methods have been devised for the implantation of fusion devices into the disc space. Both anterior and posterior surgical approaches have been used for interbody fusions. In 1956, Ralph Cloward developed a method and instrumentation for anterior spinal interbody fusion of the cervical spine. Cloward surgically removed the disc material and placed a tubular drill guide with a large foot plate and prongs over an alignment rod and then embedded the prongs into adjacent vertebrae. The drill guide served to maintain the alignment of the vertebrae and facilitated the reaming out of bone material adjacent the disc space. The reaming process created a bore to accommodate a bone dowel implant. The drill guide was thereafter removed following the reaming process to allow for the passage of the bone dowel which had an outer diameter significantly larger than the reamed bore and the inner diameter of the drill guide. The removal of the drill guide left the dowel insertion phase completely unprotected.
More recent techniques have advanced this concept and have provided further protection for sensitive tissue during disc space preparation and dowel insertion. Such techniques have been applied to an anterior approach to the lumbar spine. In one approach, a unilateral template has been provided to evaluate the space in the disc space. For bilateral implant placement, the template entire device must be rotated and visually aligned to approximately 180 from the previous position. Thus, there is the chance for operator error in rotating the device to the correct position. Further, there is little
More recent techniques have advanced this concept and have provided further protection for sensitive tissue during disc space preparation and dowel insertion. Such techniques have been applied to an anterior approach to the lumbar spine. In one approach, a unilateral template has been provided to evaluate the space in the disc space. For bilateral implant placement, the template entire device must be rotated and visually aligned to approximately 180 from the previous position. Thus, there is the chance for operator error in rotating the device to the correct position. Further, there is little guidance to ensure proper alignment of cutting instruments extending through the template.
One approach to provide such alignment is the use of a guide wire extending through a cannulated cutting instrument, such as a trephine. However, for instruments with hollow cutting heads, there is typically no engagement between the inner walls of the hollow cutting head and the guide wire. Thus, the guide wire may bend between the portion extending into the tissue and the guide wire entrance into the cannula of the instrument. As a result, the hollow cutting head may not remain in substantial alignment with the guide wire, resulting in improper opening formation. Therefore, there remains a need for improved guiding mechanisms for cutting instruments.
Once an initial opening or openings have been made in the disc space, the height of the disc space is normally distracted to approximate the normal height. Typically, a first distract or with a height estimated by CT or MRI examination is inserted. If additional distraction is required, the first distractor is removed and a second, larger distractor is inserted. However, since the positioning of the distractors is usually performed without the benefit of protective guide sleeves, the switching of distractors increases the potential for damage to neurovascular structures and may increase the time of the procedure.
For bilateral procedures, a double barrel sleeve may be inserted over a pair of previously placed distractors with a central extension extending into the disc space to maintain distraction. One limitation on guide sleeve placement is the amount of neurovascular retraction that must be achieved to place the guide sleeves against the disc space. For some patients, a double barrel sleeve may not be used because there is insufficient space to accept the sleeve assembly. Further, although the distal end of the sleeve assembly may be configured to engage the vertebral surface, if material has been removed from the disc space, there is the potential that adjacent neurovascular structures may encroach on the working channels in the disc space, resulting in damage to these structures caused by contact with instruments. While visualization windows on the guide sleeve may assist in better visualization of procedure steps and verifying unobstructed working channels prior to tool insertion, the windows themselves may allow tissue to come into contact with instruments in the working channels. Thus, there remains a need for guide sleeves requiring reduced neurovascular retraction for proper placement and providing greater protection to adjacent tissue.
With guide sleeves in place, the disc space and end plates may be prepared for receipt of an implant. Typically, cutting instruments are advanced to remove disc material and bone. Such operations may be time consuming since it is often necessary to adjust depth stop equipment and to remove the instruments to remove cutting debris. Since it is desirable to shorten the time of the operative procedure, there remains a need for improved cutting instruments and depth stop mechanisms.
While the above-described techniques are advances, improvement is still needed in the instruments and methods. The present invention is directed to this need and provides more effective methods and instrumentation for achieving the same.
The present invention relates to methods and instrumentation for vertebral interbody fusion. In one form, the method contemplates gaining access to at least a portion of the spine, marking the entrance point or points in the disc space, creating an initial opening in the disc space through a template, distracting the disc space and positioning an outer sleeve defining an interior working channel adjacent the disc space. In a preferred embodiment, the template can be inserted in a reduced sized configuration, with a first portion engaging the tissue. The template may then be manipulated to a larger configuration for bilateral insertion procedures by movement of a second portion, without repositioning the first portion. Additionally, a template according to the present invention may include trephine guides that accommodate a variety of different diameter trephine cutting heads. Specifically, trephines according to the present invention may include an upper shaft having a uniform diameter regardless of trephine cutting head diameter. Thus, the upper guides of the template maintain the trephine in axial alignment regardless of whether the lower guide engages the trephine head. In another aspect of the invention, an improved guide member is provided to maintain alignment of cutting instruments.
Once an initial opening or openings have been defined in the disc space, a distractor may be inserted to distract the disc space to the desired height. Various distractors according to the present invention may be used to distract the disc space. One such distractor has a first position that provides a first working distraction height in the disc space and a second position that provides a greater second working distraction height. Should the first working distraction height be insufficient, the distractor according to the present invention may be rotated one quarter turn to create a second greater distraction height in the disc space. Additionally, in a further preferred aspect of the invention, a modular distractor mechanism according to the present invention may be configured to accept many different rotatable distractor tips and may releasable engage the tips such that a distractor tip may be left in the disc space while permitting withdrawal of the distractor tool shaft. With such a configuration, a single distractor tool shaft may be use with various tips, thereby limiting the total number of complete distractor instruments required. Additionally, distractor tips may be made of radiolucent material that will not inhibit x-ray imaging of the disc space. Such distractor tips may include radiographic markers to indicate the ends and/or outer edges of the device and markers to indicate the rotational alignment of the distractors in the disc space.
Once the desired distraction of the disc space has been achieved, the handle of the distractor may be removed and an outer sleeve positioned over the distractor. For a bilateral approach, one or both of the distractors may be left in position and a double barrel sleeve positioned over the distractors and advanced toward the disc space. A further step that may be performed in a preferred embodiment is to select a removable distal tip for the outer sleeve that matches the height of disc space distraction and the diameter of the implant. Thus, an outer sleeve may be used with interchangeable distal tips to accomplish the insertion. Whether single or double, the sleeve is advanced until the leading distractor portion of the outer sleeve is adjacent the disc space. If necessary, a driving cap may be positioned over the proximal end of the outer sleeve. The outer sleeve is then driven into position, preferably with a spike or series of spikes engaging vertebrae adjacent the disc space.
Although various sleeves are known in the art, in a preferred embodiment, outer sleeves according to the present invention have a reduced width portion adjacent the distal end to limit the amount of retraction of the surrounding vascular and neural structures required for the procedure. In a preferred form, a double barrel sleeve assembly includes a central distraction flange having a first height and an opposing pair of lateral extensions having a second height, less than the first height. The lateral extensions provide protection from encroachment of tissue into the working area in the disc space. A further aspect of a preferred embodiment includes the provision of visualization windows along the outer sleeve for visual access to the interior working channel while instruments are in the working channel. Various combinations of windows are disclosed to accomplish the desired visualization. While visualization is desirable, having openings in the outer sleeve may allow surrounding vessels and tissue to migrate into the working channel of the outer sleeve. Tissue and vessels present in the working channel may be damaged by insertion and removal of the tools (often with cutting edges) or during use of those tools. Thus, the present invention contemplates covers over the windows that may be selectively opened for visualization and closed to prevent tissue and vessel infiltration. Additionally, the covers or the outer sleeve may be transparent to allow visualization through the windows without removing the covers or directly through the sleeve. In a similar manner, an image guidance system such as that available under the tradename STEALTH may be used in conjunction with the present system to monitor the advancement and positioning of instruments and implants. Even without the use of an imaging system, the present invention discloses the use of manually adjustable depth stop that may be used to control the steps of trephining, reaming, tapping, and dowel insertion. The term dowel is used in a broad sense throughout the disclosure and is intended to encompass dowels made of bone, metallic cages and other implants used for interbody fusion regardless of shape or material of construction.
One aspect of the present invention comprises an outer sleeve with a visualization window disposed adjacent a distal end and a cover removably covering the window. In one preferred embodiment, the cover includes a flange adjacent the distal end to mobilize vessels and other tissue away from the ends of the outer sleeve. In one form, the cover is slidably disposed on the upper surface of the tube or tubes to cover only the upper windows. In another form, the cover is slidably positioned on the tube to cover the upper and lower windows of the tube.
In yet another aspect, the outer sleeve has a double barrel configuration. The bone engagement end of the outer sleeve includes a first flange having a first height sufficient to maintain distraction. Preferably, the bone engaging end also includes a pair of opposing lateral extensions having a second height less than the first height. The lateral extensions are intended to inhibit lateral encroachment of tissue into the working area in the disc space but are not limited to maintain distraction.
Another aspect of the present invention comprises an adjustable stop mounted on a tool shaft. The stop is selectively engageable with the tool shaft at a plurality of locations along the tool shaft by axial movement of a collar to control the position of the stop engaging portions. With the collar in a first position, the engaging portions are disengaged from the tool space. With the collar in a second position, the engaging portion is urged into engagement with the shaft. The tool shaft is sized to be received within an outer sleeve and the stop is sized to prevent passage within the outer sleeve. Thus, the stop may be selectively coupled to the tool shaft to control the extent of tool shaft that may be received within the outer sleeve. Although not required, in one embodiment the stop includes a viewing window and the tool shaft includes markings, whereby the markings are calibrated to indicate to the user the extent of tool shaft extending beyond a distal end of the outer sleeve.
Still another aspect of the invention comprises a reamer with a reaming head having a plurality of reaming apertures in communication with an internal channel. The internal channel extends within the reaming head and proximally along at least a portion of the reamer shaft. The internal channel includes a proximal segment extending nonparallel to the longitudinal axis of the reamer shaft, whereby reaming debris may be transferred to the exterior of the reaming shaft.
The present invention further contemplates a method for interbody fusion comprising, positioning a template adjacent a fusion site, forming at least one initial opening in the disc space, distracting the disc space, placing a distal portion of an outer sleeve into the disc space, the outer sleeve including at least one visualization window and cover removable disposed over the windows and visualizing the surgical site through the windows. Preferably, the method also includes removing the cover to expose the window prior to visualization. Further, the method may include the step of enlarging the opening with cutting tools and may further include attaching an adjustable depth stop to the tool shaft prior to extension beyond the distal end of the outer sleeve.
Related objects and advantages of the present invention will be apparent from the following brief description of the drawings.